Post-irradiation modification of oxygen-dependent and independent damage by catalase in barley seeds.

If H2O2 is one of the major mediators of the 'oxygen effect' in biological systems then catalase, which enzymically decomposes H2O2 should have a significant influence on radiation damage, particularly under oxygenated conditions. The post-irradiation (300 Gy gamma rays) effect of catalase was, therefore, assessed on barley seeds of about 4 per cent moisture content under oxygenated and oxygen-free conditions at varying temperatures. Catalase affords concentration-dependent radioprotection under oxygenated condition at both 25 degrees C and 4 degrees C. The level of protection at 4 degrees C is less than at 25 degrees C. This is obviously due to a decrease in catalase activity at low temperature. Under oxygen-free conditions, catalase enhances radiation damage at 4 degrees C while at 25 degrees C it has no effect. This has been substantiated by data on the frequency of chromosomal aberrations and on peroxidase activity. Sodium azide, a catalase inhibitor, was found to eliminate the radioprotective action of catalase. The study supports the view that the 'oxygen effect' is mediated largely through peroxides in irradiated biological systems. However, the observations made particularly at 4 degrees C under oxygen-free condition seem to involve physicochemical reactions.